Power converter circuits, for example, resonant power converters, basically include switching circuits, transformers, and rectifying diodes. In a conventional resonant power converter, the switching circuit is connected to a primary winding of the transformer and is regulated by a control circuit to turn on or off. The transformer is configured to receive electric energy through its primary winding and transfer the received electric energy to its secondary winding by electromagnetic inductance. The rectifying diodes are connected to the secondary winding of the transformer for rectifying the AC voltage induced across the secondary winding into a DC voltage, thereby powering a load by the rectified DC voltage.
Nonetheless, the forward-conducting voltage drop across the rectifying diodes will cause a considerable conduction loss for rectifying diodes. Consequently, the synchronous rectifier that is implemented by transistors had replaced the rectifying diodes in a power converter. Compared to conventional power converters using rectifying diodes, the power converters using synchronous rectifiers can reduce the power loss significantly.
Despite that fact that the power loss of the power converters can be decreased by employing a synchronous rectifier to perform power rectification, a precise control mechanism is required to ensure the accurate turn-on and turn-off of the synchronous rectifier that is implemented solely by transistors. The contemporary control mechanism for the synchronous rectifier is accomplished by a control integrated circuit to control the turn-on and turn-off of the synchronous rectifier. In addition, the control integrated circuit is able to sample the voltage difference between the drain terminal and the source terminal of the synchronous rectifier to calculate the current flowing through the synchronous rectifier, thereby manipulating the synchronous rectifier to turn off.
Nonetheless, the aforesaid control mechanism is subjected to the leakage inductance on the circuitry of the power converter. The effect arising from the leakage inductance would prohibit the control integrated circuit from accurately sampling the voltage difference between the drain terminal and the source terminal of the synchronous rectifier, and would further prohibit the control integrated circuit from accurately manipulating the synchronous rectifier. Such circumstances would result in the fallout that the synchronous rectifier may be turned off in advance. In this way, the synchronous rectifier is prone to be burnt down and the overall efficiency of the power converter is deteriorated.
Therefore, it is an imminent tendency to develop a power converter and a control method applied to the synchronous rectifier of the power converter such that the aforesaid deficiencies and disadvantages can be addressed.